1. Field
The present invention relates to a solid-state image device having pixels for focus detection.
2. Description of the Related Art
In recent years, generally, video cameras and electric cameras using a solid-state image device of CMOS type are widely gaining popularity. In the solid-state image device of CMOS type, a plurality of pixels having photoelectric conversion parts for converting a received light into an electronic signal are allocated in a two dimensional array. Regarding an electric charge accumulated in the photoelectric conversion part of each pixel, the address of each pixel is selected by a vertical scanning circuit, and signals from pixels of one row are read to a horizontal output circuit via vertical signal lines. The signals from pixels of one row read to the horizontal output circuit are output to the outside in sequence column by column by a horizontal scanning circuit.
On the other hand, a general camera system has an auto-focus function to perform focusing of a camera lens automatically, for which a dedicated focus detection device for detecting a focus is used. However, a dedicated focus detection device and an optical system for focus detection to guide a light thereto are required, and this hinders cost reduction and downsizing of cameras.
Accordingly, to make it possible to perform focus detection with the solid-state image device by split-image phase difference method (also called split-image method or phase difference method) without using the dedicated focus detection device, there is proposed a solid-state image device in which pixels for focus detection are embedded in an ordinary solid-state image device (for example, refer to Japanese Unexamined Patent Application Publication No. 2000-156823).
In a conventional solid-state image device in which pixels for focus detection are embedded, signals for focus detection read from the pixels for focus detection are read together with image signals via a circuit which reads normal image signals.
However, when it is desired to read the signals for focus detection quickly, the signals for focus detection cannot be retrieved unless image signals of all the pixels in the solid-state image device are read once. As a result, reading of the signals for focus detection takes time, which causes a problem that a high-speed auto-focus function cannot be realized.